Rehabilitation of the Second Lower Feeder

Abstract

The Metropolitan Water District of Southern California (MWD) is a consortium of 26 cities and water districts that provides drinking water to nearly 19 million people in parts of Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties. Metropolitan currently delivers an average of 1.7 billion gallons of water per day. Metropolitan has 830 miles of pipelines, of which 163 miles are Prestressed Concrete Cylinder Pipe (PCCP) lines. The lines are distributed throughout Metropolitan’s service area in both urban and rural areas. The pipelines range in diameter from 54 to 201 inches and operate at pressures up to 340 psi. Metropolitan’s PCCP was constructed between the early 1960’s through the mid1980’s. In 2000, Metropolitan initiated its PCCP assessment program. It included inspection of all 163 miles of PCCP lines using electromagnetic and visual inspection methods. Since that date, electromagnetic inspections have been performed annually during the winter shutdown season, with an average of 35 to 40 miles inspected every year. Every year the results of these electromagnetic inspections are reviewed and pipe considered to be at high risk of failure is repaired. A total of 7,534 feet of pipe or 378 pipe segments have been repaired since 1999 at a total cost of approximately $65 million dollars. Metropolitan has recently changed its asset management philosophy of PCCP from an inspection driven reactive method to a systematic replacement of its most at risk pipelines. This paper will discuss the first planned systematic replacement of one of its PCCP pipelines - the Second Lower Feeder. The Second Lower Feeder (SLF) has 29 miles of PCCP. The pipeline varies in diameter from 84 inches to 78 inches. This paper will discuss: the reasons for the change in philosophy of the asset management approach; the technical challenges faced by the project such as loss of hydraulic capacity; the approach to scheduling long shutdowns; prioritization and sequencing of the relining effort; and the various replacement options considered.